There is mounting evidence that incorporation of antineoplastic drugs into carrier liposomes may circumvent such problems as toxic side effects, tumor resistance and immunologic reactions associated with conventional cancer chemotherapy. The objective of the proposed experiments is to examine some basic properties of liposomes and to study the mechanisms by which they interact with one another and with living cells. Experiments will be directed towards finding systems in which liposome-liposome or liposome-cell fusion is the major pathway of interaction. A study of liposome-liposome interactions in simple model systems, and liposome-cell interactions in vitro will hopefully provide us with data enabling us to maximize in vivo uptake of liposomes and delivery of their contents to cells. The long-term goal of these studies is to advance our understanding of the physical nature and properties of liposomes to the point where they can be used effectively for the treatment of cancer in vivo. The studies proposed here will be coordinated with related studies already under way to incorporate target molecules into the liposome bilayer enabling the phospholipid vesicles to be directed to, and deliver their contents to, specific cell types.